It is often necessary or desirable for a person to exercise a particular muscle or group of muscles. For example, when a muscle is damaged, such as through injury or surgery, it is important to exercise the muscle to prevent atrophy and to strengthen the muscle for normal use. Further, people exercise healthy muscles to increase strength and to maintain an active and healthy lifestyle, as well as to improve their appearance. Various routines have been developed to exercise different muscle groups by forcing the muscles to contract and extend under a load, such as by moving a free weight or doing chin ups against the force of gravity or by moving a handle whose movement is resisted by an exercise machine.
One such exercise to work the back muscles is known as a chin up. The exerciser grasps a fixed overhead bar or handle in a military or overhand grip and pulls himself upward against his bodyweight or against his bodyweight plus added weights. Even if done properly, this exercise may not permit a full range of exercise since the exerciser may only pull part way up and stop before the back muscles have contracted fully. When doing a chin up, the resistance provided by gravity is constant while the strength of the muscles varies over the range of motion. Consequently, the muscles are not fully loaded at each point over the range. During a chin up exercise, the hands seek to follow a curved path outward as the body is pulled upward. This path cannot be followed during a chin up because the hands are maintained at a fixed distance apart.
To overcome these difficulties, lat pulldown machines have been developed that simulate the exercise movements of a chin up. In one apparatus marketed by the assignee of the instant application, a user exercises by pulling a grip bar down toward his shoulders. A seat and knee pad are mounted to a frame to position a user. A grip bar contains angled handles for gripping by a user. A cable connected to the middle of the grip bar operably connects the arms to a weight stack such that when a user pulls down on the grip bar, the weight stack is lifted and provides resistance to the exercise. The cable may be journaled over a variable radius cam to alter the distance the weight is displaced for a given distance of grip bar movement at a particular point in the range of motion. Consequently, the resistance to the movement of the handles can be varied to match the strength curve of the back muscles. While this apparatus has solved many problems associated with performing lat pulls with barbells and dumbbells, it does not permit the user to vary the distance between his hands while performing the exercise.
In both the chin-up exercise and the traditional lat pull-down machine, it is difficult to isolate the latissimus dorsi muscles of the back because an exerciser tends to also use the bicep muscles of the arm. One solution is to use a wide hand placement, but this reduces the range of motion through which the latissimus dorsi are worked, because these muscles are already partially contracted in the starting position.